Catalytic dehydrogenation of hydrocarbons



Patented Oct. 25, 1949 CATALYTIC DEHYDROGENATION OF HYDROCARBON S WalterA. Schulze and John C. Hillyer, Battlesville, Okla, assignors toPhillips Petroleum Company, a corporation of Delaware No Drawing.

Original application June 21, 1943,

I Serial No. 491,702. Divided and this application May 5, 1947, SerialNo. 746,166

' 8 Claims. 1

The present invention relates to the catalytic dehydrogenation ofhydrocarbons, for example, dehydrogenation of olefins .to diolefins,alkylbenzene to alkenylbenzenes such as ethylbenzene to styrene, andsimilar reactions. In a more particular aspect the present inventionrelates to a process for the conversion or dehydrogenation of suchhydrocarbons utilizing a new and improved multi-component catalystcomposition.

It is therefore an object of the present invention to provide animproved process for the catalytic dehydrogenation ofhydrocarbons,particularly for the dehydrogenation of butenes to 1,3- butadiene,ethylbenzene to styrene, and similar dehydrogenation of hydrocarbons tohydrocarbons of lower degrees of unsaturation.

It is a further object of the invention. to provide an improved processfor the dehydrogenation of hydrocarbons such as butenes, utilizing animproved multi-component catalyst.

Other objects and advantages of the invention, some of which arespecifically ref-erred to hereinafter, will be apparent to those skilledin the art.

The present application is a division of application Serial No. 491,702filed June 21, 1943, U. S. Patent 2,431,427, issued November 25, 1947,entitled Dehydrogenation catalysts.

A preferred catalytic composition of the invention is a pelletedalumina-base catalyst associated with oxides of barium, magnesium andpotassium. The advantages of the pelleted catalyst include uniform sizeand lowered pressure drop in the catalyst case where low operatingpressures are desirable. However, bauxite may serve as a source of thealumina used as the catalyst base, with suitable treatment to activateand preferably to remove iron and silica impurities.

Preferred catalytic compositions of the present invention are thosewhich are included in the following ranges:

Component: Weight per cent Barium Hydroxide 4-6 Magnesium oxide 2-4Potassium hydroxide 4-6 Alumina Remainder While the functions of theindividual components of the catalyst composition are not limited to anyparticular theories, the alumina is often regarded as the basic catalystwith certain of its catalytic properties modified by the addedingredients. The modifications may be directed toward improving theconversion eificiency by either suppressing undesirable transformationsor prolonging the practical conversion period. Specific modification inthis case also is directed toward improved catalyst characteristics forthe reactivation operation that is car ried out with anoxygen-containing reactivation as.

The finished catalyst composition also possesses high activity in thepresence of steam which is used as diluent during either the processingor reactivation steps. This water-resistant feature is inherent inalumina and is substantially imto promotion of the water-gas reactionbetweensteam and carbon by the potassium hydroxide.

The catalyst compositions of the invention may be prepared by:

(1) Dry mixing and pelleting of dry ingredients followed by heat orother treatment necessary to convert the components of the compositionto the desired form.

(2) Impregnation of alumina pellets with a solution of the metal saltsor hydroxides, followed by drying or calcination, and

(3) Wet mixing of the ingredients followed by extrusion and drying inpills of suitable size.

Of these three methods, the first two produce catalysts of superiormechanical strength, porosity and catalytic activity. The impregnationmethod (method 2) is preferred to the first in some cases because thecatalyst activity and mechanical strength are higher. However, withproper calcination, etc., the dry-mixed pellets may be brought to highactivity.

Preferred methods of preparing the catalysts of the present inventionare illustrated by the following preparations:

Preparation A Alumina trihydrate substantially free of iron is calcinedat about 650 F. until the water content is reduced to 9 to 12 per centby weight. The partially dehydrated alumina is then mixed with magnesiaand barium carbonate in the following proportions and pelleted with theaid of a small amount of a fatty acid or fatty acid soap as a lubricant:

Component: Parts by weight Alumina (A1203) 21.8 Magnesia (MgO) 0.7Barium Carbonate (BaCOa) .1.3

The resulting pellets are calcined at approximately 1100 F. to removeWater, carbon dioxide and lubricant. The calcined pellets are thentreated with suflicient potassium hydroxide (KOH) solution to add thedesired weight of KOH and dried. Subsequent calcination gave a catalystpreparation of the following composition, on a dry basis.

Component: Per cent by weight Alumina (A1203) 86.0 Magnesia (MgO) 3.1Barium hydroxide (Ba(OH)z) 5.?

Potassium hydroxide (KOH) 5.2

Preparation B (3) 'A final impregnation with 10% potassium hydroxidesolution, followed by drying.

The finished catalyst had the following composition, on a moisture-freebasis:

Component: Per cent by weight Alumina (A1203) 85.0 Magnesia (MgO) 3.8Barium hydroxide (Ba(OH)2) 5.2 Potassium hydroxide (KOH) 6.0

Preparation C The catalyst was prepared as described in Preparation Bwith the exception that potassium carbonate solution was used in thefinal treatment instead of a solution of potassium hydroxide.

Preparation D Preparation E The desired proportions of aluminatrihydrate, magnesia, barium carbonate and potassium carbonate weremixed, lubricated with water, and extruded through dies to producepellets, The

pellets were calcined at 1100 F. to produce a catalyst with thefollowing composition:

Component: Per cent by weight Alumina (A1203) 88 Magnesia (MgO) 3 Bariumhydroxide (Ba(OH)z) 3 Potassium oxide (K20) 6 Preparation F Aluminatrihydrate pellets prepared as described in Preparation B wereimpregnated with metal salts as follows:

(1) The pellets were treated with a solution of magnesia and bariumhydroxide dissolved in acetic acid. After adsorption of requisitequantities of this solution, the pellets were calcined at 950 F.

(2)The calcined pellets bearing magnesium and barium compounds (oxidesor hydroxides) were next impregnated with potassium carbonate solutionand dried to remove water.

The finished catalyst had the following approximate composition, on amoisture-free basis:

Component: Per cent by weight Magnesia (MgO) 4 Barium hydroxide(Ba(OH)2) 5 Potassium hydroxide (KOH) '7 Alumina (A1203) 84 While theforegoing preparations exemplify preferred compositions, the proportionsof the ingredients may be varied widely. However, larger proportions ofthe modifying ingredientsare not usually needed to obtain the desiredresults, and catalyst costs may be increased without compensatingadvantages when the three materials added to the alumina amount to morethan about 10 to about 20 per cent by weight of the final composition.Final addition of potassium hydroxide or carbonate or similar alkalinepotasslum salt is usually preferred to neutralize any acidic residues inthe catalyst pellets.

While the quantities of barium and potassium hydroxides may be variedwithin the limits of approximately 3 per cent or less to approximately10 per cent or more by weight of the catalyst composition, the magnesiacontent is preferably less than approximately 5 per cent byweight. Thisquantity is sufficient to provide improved catalyst characteristics, butnot apparently great enough to introduce undesirable catalytic ormechanical properties. Large proportions of magnesia often increase theactivity of the catalyst toward cracking reactions, and the mechanicalstrength of the catalyst pills is somewhat decreased as the magnesiacontent is increased above the preferred proportions.

Untreated synthetic alumina pellets or granules when employed indehydrogenation reactions, such as in the conversion of normal butenesto butadiene, exhibit an initial period of low butadiene production,usually termed an induction period, before maximum conversion tobutadiene is reached. During this induction period, isomerization of thenormal butene to isobutene is noted, as well as formation of heavyliquid polymers. Carbon deposition upon such a single-component catalystis also relatively rapid at normally preferred operatiing conditions.

When alumina pellets are treated with barium hydroxide and magnesia,without potassium hydroxide, beneficial effects during conversion arenoted, including higher initial conversion to butadiene and decreasedisomerization and polymerization. The average conversion efliciency isthereby increased, and butadiene yields are improved.

The addition of potassium hydroxide to such an alumina-magnesia-bariumhydroxide catalyst composition produces a further unexpected improvementin dehydrogenation reactions, particularly when steam is used as aninert diluent and heat carrier to reduce the partial pressure of C4unsaturates in the reaction mixture. With the preferred multi-componentcatalyst compositions specified above, practical conversion periods arelengthened, apparently by a reduction in the rate of carbon depositionon the catalyst, and the on-stream time of each catalyst vessel isincreased. Furthermore, when reactivation is desirable, because ofprogressive diminution of or decrease in catalytic activity,reactivation is more quickly accomplished with oxygen-containing gasesthan with other catalysts that do i not contain potassium hydroxide. Apreferred reactivation procedure involves the use of mixtures of steamand air, in which some endothermic carbon-removing reactions areapparently important factors in promoting rapid reactivation withsatisfactory temperature control.

Magnesia and barium hydroxide remain undissociated at the temperaturesemployed for butadiene production and catalyst reactivation, so that thecatalyst is subject to only extremely gradual deterioration ormechanical attrition with continued use. The potassium hydroxide in thepresence of magnesia and barium hydroxide is unexpectedly stabilized andits modifying effects are substantially prolonged to correspond toultimate catalyst life, despite the high temperatures employed. This isin contrast to catalysts consisting solely of alumina and alkalimetalhydroxides, which under certain high temperature conditions usuallyundergo deteriorative changes.

The length of the conversion period with the present catalyst varieswith the hydrocarbon feed being treated and the conversion conditions.Under preferred conditions for butadiene production the conversionperiod may range from about four to twelve or more hours beforereactivation becomes necessary because of lowered conversion. Suchextended conversion periods indicate the moderate rate of carbondeposition, even at severe conversion conditions, particularly whensteam is present in relatively large proportions in the reactionmixture.

Reactivation of the catalyst is usually accomplished by burning oiicarbonaceous deposits with air, oxygen or oxygen-containing gasmixtures. The reactivation gas may comprise mixtures of steam and air ormixtures of recycle, combustion or flue gases with air. The presence ofsteam in the reactivation gas is often desirable for use with thepresent catalyst. It is preferred to control the rate of reactivation sothat the time required is substantially less than the conversion period,while maintaining temperatures between approximately l000 andapproximately 1400 F.

In the dehydrogenation of normal butenes to produce butadiene, preferredconversion temperatures for use with the present catalyst areapproximately l100 to approximately 1300 F. Hydrocarbon space velocitiesof 500 to 5000 volumes may be employed. In one modification of thecatalytic dehydrogenation step, low superatmospheric pressures are used,and it is preferred to maintain partial pressures of butene in the feedbelow atmospheric pressure. Low butene partial Example 1 A catalystprepared according to the method described in Preparation B hereinabovewas utilized in the form of inch x inch pills to dehydrogenate a mixtureof l-butene and 2-butene. The catalyst was disposed in tubes ofrelatively small diameters heated by hot flue gases from a feedpreheater. The butene charge was admixed with steam in a ratio of threevolumes of steam per volume of hydrocarbon, and the total vapor mixturewas passed through the catalyst tubes at from 1200 to 1210 F., at 3pounds gage pressure, and at a space velocity of 1300 volumes per hour.The resulting products were quenched with water, compressed andfractionated to separate C4 hydrocarbons from lighter and heaviermaterial. Butadiene was separated from unreacted butenes, and the latterwere returned to the catalytic treatment.

Analysis of products from a series of operating cycles gave the averageyield figures shown in the following table. Each cycle consisted of 8hours on processing and somewhat less than 8 hours on reactivation.

Cycle 1 6 I 12 I 16 26 Average Conversion per pass (Weight Per CentButenc Charged) Average Butadiene Yields per pass (Weight Per CentButcne Charged) Average Ultimate Butadiene Yield (Weight Per Cent ButeneCharged) ing processing amounted to about 1.0 per cent by weight of thebutene charged. Catalyst attrition (mechanical) after 550 hoursoperation was also negligible.

Example 2 Using conditions similar to those described in Example 1 andusing a catalyst inthe form of A; inch x inch pellets prepared accordingto the procedure described in Preparation D hereinabove, the followingresults were obtained. The

processing periods of 8 hours were followed by reactivation periodswhich in some cases were of only 5 to 6 hours duration. The followingtable 8 lists average conversion and yield figures for several of the8-hour process cycle periods.

Virtually no isobutene was formed in these reactions. Carbon-depositionwas reduced by the water gas reaction to 2.3 per cent by weight of thebutene charged. Carbon-removal as carbon oxides in the product streamamounted to 0.7 to 1.0 per cent by weight of the butene charged.

Inasmuch as the foregoing description comprises preferred embodiments ofour invention, it is to be understod that the invention is not limitedthereto, and that modifications and variations may be made therein toadapt the invention to other uses without departing substantiallytherefrom. The invention is to be limited solely by the appended claims:

We claim: I

1. In a process for the catalytic dehydrogenation of a dehydrogenatablehydrocarbon to a less saturated hydrocarbon the improvement whereby theyield of dehydrogenated hydrocarbon is increased, isomerizationreactions are substantially repressed, the tendency to deposit carbon isdecreased, the induction period of the catalyst is shortened and thewater resistance of the catalyst is improved; which comprises contactingthe hydrocarbon under dehydrogenation conditions with a multi-componentcatalyst composition consisting essentially of alumina formed by thedehydra tion .of hydrated alumina, together with from approximately 2 toapproximately 4 per cent by weight of magnesia, approximately 4 toapproximately 6 per cent by weight of barium oxides calculated as bariumhydroxide, and approximately 4 to 6 per cent by weight of potassiumoxide calculated as potassium hydroxide.

2. A process according to claim 1 wherein butene is dehydrogenated toform butadiene.

3. A process according to claim 2 wherein a butene is dehydrogenated toproduce butadiene at a temperature within the range of approximately1100 to approximately 1300 F.

4. A process according to claim 1 wherein an alkylbenzene isdehydrogenated to form the corresponding alkenylbenzene.

5. A process according to claim 4 wherein ethylbenzene is dehydrogenatedto form styrene.

6. A process for the dehydrogenation of dehydrogenatable hydrocarbons toform hydrocarbons having lower degrees of saturation "which comprisescontacting said hydrocarbons under dehydrogenation conditions with acatalyst consisting essentially of alumina formed by the dehydration ofhydratedalumina together with from approximately 2 to approximately 4per cent by weight of magnesia, approximately 4 to approximately 6 percent by weight of barium oxides calculated as barium hydroxide andapproximately 5 to approximately 6 per cent by weight of potassium oxidecalculated as potassium hydroxide.

7. A process according to claim 6 wherein the catalyst consistsessentially of alumina formed by the dehydration of hydrated aluminatogether with approximately 4 per cent magnesia, 5 per cent bariumoxides-calculated as barium hydroxides, and approximately 6 per cent byweight of potassium oxide calculated as potassium hydroxide.

8. A process according to claim '7 wherein butene is dehydrogenated toform butadiene.

WALTER A. SCHULZE.

JOHN C. HILLYER.

REFERENCES CITED UNITED STATES PATENTS Name Date Schulze et a1 Dec. 25,1945 Number

